1. Field of the Invention
The present invention relates to a process for the production of aldehydes of the general formula R--CH(CH.sub.3)CHO by reacting olefins of the general formula R--CH.dbd.CH.sub.2 with carbon monoxide and hydrogen at an elevated temperature and elevated pressure in the presence of rhodium complex catalysts containing phosphine.
2. Discussion of the Prior Art
The so-called Oxo synthesis (hydroformylation) is widely used in industry for the preparation of aldehydes and alcohols. Cobalt which is active in the form of its carbonyl compounds is used above all as catalyst for the reaction of the olefin with carbon monoxide and hydrogen on a commercial scale.
More recently, rhodium complex catalysts in which biphilic ligands such as tertiary phosphines are coordinated the rhodium atom are used for the hydroformylation, especially for the hydroformylation of specific olefins. Rhodium catalysts are characterized by high selectivity for the formation of straight-chain aldehydes and permit the reaction to be carried out under a lower pressure than in conventional processes.
According to German Offenlegungsschrift (DOS-OS) No. 17 93 069, oxygen-containing products which are rich in normal aldehydes are prepared by reacting an .alpha.-olefin compound with carbon monoxide and hydrogen in the presence of a catalystic amount of a complex catalyst which consists substantially of rhodium complexed with carbon monoxide and a ligand which contains a trivalent atom of a Group V element, said atom being substituted with three organic radicals. The ligand is characterized inter alia in that it exhibits a free electron pair and has a .DELTA.-HNP value of at least 425 and preferably at least 500. The .DELTA.-HNP value is a measure of the basicity of the ligand, high basicity corresponding to a low .DELTA.-HNP value. The reaction is carried out at 50.degree. to 145.degree. C. and a total pressure of carbon monoxide and hydrogen of less than about 31.5 atmospheres gauge.
The advantages of the oxo reaction catalyzed by rhodium complex compounds, especially the use of low pressure and high yields of straight-chain aldehydes, are offset inter alia by the requirement to use large reaction spaces and the difficulty to recover aldehydes which are methyl-branched in alpha position in satisfactory yields at high purity.
It is an object of this invention, therefore, to provide a process by means of which higher aldehydes which are branched in alpha-position, i.e., aldehydes having at least 10 carbon atoms can be prepared in a simple manner.